In an assembly process of a semiconductor device (hereinafter, also referred to as a “package”), a method in which a bonding wire is electrically connected by thermocompressing between an aluminum electrode of an element (hereinafter, also referred to as a “chip”) and an inner lead of a lead frame, is currently the mainstream. In recent years, high integration and a trend toward multi-pin electronic components have been proceeding every year with market trends for a miniaturization, weight reduction, and improved performance of electronic devices. Therefore, more complex wire bonding processes are required than before, and oxidation of a copper surface is more progressed when a lead frame made of copper is used since the lead frame made of copper is exposed for a long time at high temperatures of 200 to 250° C.
Under these circumstances, even an encapsulating material with excellent adhesion to unoxidized copper surface in the related art has poor adhesion to copper of which a surface is oxidized differently in many cases, resulting in problems such that separation occurs at the interface between an encapsulating resin cured substance and a lead frame at a time of die-cutting after resin encapsulant molding or solder reflowing.
Improving adhesion between an inserted substance such as a lead frame and an encapsulating resin cured substance in order to suppress the separation conflicts with improving mold releasing property to a mold of the encapsulating resin cured substance, therefore, there have been problems such that moldability is reduced when the adhesion to the inserted substance such as a lead frame is improved since a mold releasing property from the mold is deteriorated.
Before oxidation of a lead frame made of copper due to the high integration of electronic components becomes a problem, a method in which oxidized polyethylene wax, and a compound in which a copolymer of 1-alkene and maleic acid is esterified are added and used in combination as a mold releasing agent in order to balance adhesion and a mold releasing property has been proposed (for example, see Patent Documents 1 and 2). According to this method, adhesion and a mold releasing property to unoxidized copper are excellent, however, there has been a problem that adhesion of an encapsulating resin to an oxidized copper frame is reduced since oxidized polyethylene wax is used as a combination. In addition, if the compound in which a copolymer of 1-alkene and maleic anhydride is esterified is used alone, a mold releasing property is insufficient and a continuous moldability has not necessarily been sufficient in some cases.